Printer with print wheels having coded perforations for selective positioning

ABSTRACT

A printer is disclosed wherein the print wheels are positioned individually to desired symbols through coding provided in the form of perforations in the print wheels themselves. After individually positioning the print wheels, one at a time in sequence, by sensing the code perforations in a turning wheel through sensing perforations in all other wheels held stationary, a print roller is driven over the selected symbols.

United States Patent [191 Ambrosio Mar. 25, 1975 1 PRINTER WITH PRINTWHEELS HAVING CODED PERFORATIONS FOR SELECTIVE POSITIONING [75]Inventor: Biagio F. Ambrosio, Woodland Hills, Calif.

[73] Assignee: Electronic Memories 81. Magnetics Corporation, LosAngeles, Calif. [22] Filed: Dec. 13, 1973 Appl. No.: 424,454

[52] US. Cl Nil/93.29, 197/18/101/110 [51] Int. Cl B41] 7/34 [58] Fieldof Search 101/93 C, 95, 99, 45, 110,

[56] References Cited UNITED STATES PATENTS 3,229,626 H1966 Arps.;.i01/93c 3,334,237 8/1967 Dodsworth et a1. 250/219 3,613,574 10/1971Longcoy 101/110 X 3,669,016 6/1972 Kittel 101/110 X 3,673,957 7/1972Guzak 101/93 C Primary Examiner-Edgar S. Burr Assistant Examiner-EdwardM. Coven Attorney, Agent, or Firm-Lindenberg, Freilich, Wasserman, Rosen& Fernandez [57] ABSTRACT A printer is disclosed wherein the printwheels are p0- sitioned individually to desired symbols through codingprovided in the form of perforations in the print wheels themselves.After individually positioning the print wheels, one at a time insequence, by sensing the code perforations in a turning wheel throughsensing perforations in all other wheels held stationary, a print rolleris driven over the selected symbols.

10 Claims, 6 Drawing Figures PATENTEDHAR25|975 872,789

sum 1 [E 3 I E PAPER .rUPPLy F011. 7

PATENTEHNAR25|975 sum 3 or 3 PRE , 1 PRINTER WITH PRINT WHEELS HAVINGCODED PERFORATIONS FOR SELECTIVE POSITIONING BACKGROUND OF THE INVENTIONI This invention relates to improvements in printers, and moreparticularly to improvements in low cost printers.

In the field of high-speed printers, a technique which has beensuccessfully exploited is the provision of a rotating drum on which thesymbols to be printed are provided with one complete set of all symbolscircumferentially disposed, one set for each column of information to beprinted. Identical symbols are aligned in a row parallel to the drumaxis in order that printing of the same symbol in every column in whichit is to appear can be effectuated at one time. Consequently, to printany given symbol in selected columns, the proper position of thecharacter drum is detected as it continues to rotate, and print hammersfor the selected columns are energized, thus printing the symbol whereneeded in a line of printed information.

The symbol to be printed is detected at the print station by eithercounting symbols from an index position, or by detecting a unique codeon a disc or cylinder at tached to the shaft to rotate with the drum.High speed printing is achieved because a line of information is printedeach time the drumcompletes one revolution without stopping. Inpractice, that is done by comparing separately the position of thedrum'with the symbol to be printed at each column. When the symbol to beprinted at any given column comes up to the print station, a printhammer is energized to print that symbol in that column. Perforations inthe disc or drum are often used to implement the code because of theirpermanency and the ease with which they can be detected optically.

Such high-speed printers are much too expensive for general use. A majorcost factor is the need for a separate print hammer for every column.Due to the dynamics of printing with a hammer, the hammer must beproperly designed and produced with precision. Otherwise, the hammer maysmear the symbol being printed if it dewlls too long, or cause a ghostof the symbol to be printed if it bounces upon impact. For slowprinters, it would be desirable to use separate print wheelsindividually set for the line of information to be printed. Once set, amoveable platen may be employed to print the entire line of information.

Many printing calculators have been provided with low cost printers inwhich the positioning of the print wheels has been effectuated as anintegral part of the calculations. Others may have mechanial means forstepping each print wheel individually from an index position common toall after calculations are complete. What is needed is an inexpensivetechnique for positioning print wheels individually at a reasonably fastrate without dependence on any other operations, aside from providingthe information to be printed in a digital code.

SUMMARY OF THE INVENTION An object of this invention is to provide animproved low-cost printer for use in any system to print informationprovided electronically in digital code.

Still another object is to provide an inexpensive system for aligningindividual print wheels for each line of information to be printed inresponse to digital codes '2 representing symbols to be printed in theposition of each print wheel.

These and other objects of the invention are achieved by providing avplurality of print wheels, each with symbols on the circumferentialsurface thereof and V notches on that surface between symbols used forholding the print wheel in an indexed position with a symbol in properalignment with symbols of all other print wheels at a print station.Each print wheel is provided with two sets of perforations, each setcomprising a plurality of grouped perforations, each group having one ormore perforations in a fixed pattern of perforations. All groups of oneset have at least N perforations for use only as light paths in sensingcoded groups of the other set in one rotating print wheel while allother print wheels are latched in an indexed position. The

perforations in N perforation positions of the groups in the second setin the same pattern as the N perforation positions of groups in thefirst set are provided in accordance with a predetermined code touniquely identify the positions of symbols on the print wheel. Inoperation, all perforations of groups of the first set in one wheel areinline with all groups of the first set of all other wheels whilelatched, and perforations of one group of every wheel will be in line toform N light beam paths from a source, or sources, illuminating all Nperforations of a group on a wheel at one end and N photocells each ofwhich is positioned opposite one of N perforations ofa groupon a wheelat the other end.

To select a symbol on a given print wheel, that print wheel is unlatchedand caused to rotate by a motordriven shaft through a friction clutch,thus causing code groups on that wheel to be driven past the alignedperforations of the remaining print wheels at rest until the code of thedesired symbol is detected by the photocells. The latching means for theprint wheel being set is then caused to again latch. The position of thelatching means relative to the sensing position stops the print wheelwith the selected symbol in the print position. The V notch into whichthe latching means fits assures the selected symbol will come to rest inproper alignment at the print station. When all print wheels have beenindividually set, a print roller is driven across the selected symbolsat the print station, thus applying pressure on paper against theselected symbols for printing the symbols on the paper.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionwill best be understood from the following description when read inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 discloses the organization of aprinter embodying the principles of the present invention.

FIG. 2 is a side elevation of a print wheel and latching platerepresentative of the arrangement for each of the print wheels in FIG.1.

FIG. 3 is an isometric view of a complete arrangement for the latchingplate and actuating means of FIG. 2. 1

FIG. 4 illustrates in perspective the arrangement of photodetectingmeans for detecting a coded group of perforations in one rotating printwheel through aligned sense perforations in stationary print wheels.

FIG. 5 illustrates in a block diagram the electronic system forspecifying the symbols to be selected for printing in each of the printwheels of FIG. 1.

FIG. 6 is a circuit diagram for the control of a motor which drives aprint roller in the arrangement of FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I in moredetail, there is shown an exemplary arrangement of apparatus forprinting in accordance with the present invention. A plurality of printwheels 10 through 10- are supported by a motor driven shaft 11 andengaged for rotation with the shaft through a slip clutch 12 (FIG. 2).Each print wheel is held in a stationary position by a separate latchingmeans consisting of a plate l3 of non-magnetic material with a pointedarm 14 engaging a V notch, as is morev clearly shown in FIG. 2. A spring15 holds the plate 13 in the latching position.

Once all of the print wheels have been selectively positioned, thesymbols at the print station are printed on paper supplied from a roll16. The printing is done by driving a roller 17 between guides 18 and 19extending across all the wheels at the print station. The paper isimpressed on the raised symbols of the print wheels.

Carbon orv ink ribbon 20 is supplied between the paper and the printwheels if pressure-sensitive paper is not used.

Each print wheel has a number of raised portions, one for each symbolsuch as the numerals 1 through 9 and 0 to be selectively printed. Eachprint wheel also has two interspaced sets of perforations, oneset-consisting of groups of four sense holes disposed on evenly spacedsectors; and more particularly on spaced radial lines. one group ofholes for each symbol position, such as a group 21. The other setconsists of groups of code holes disposed on intermediate sectors spacedin the same pattern, namely radial lines. Thus, one code group for eachsymbol is interspaced between two groups of sense holes, such as a groupof senseholes 22.

When at rest, the four holes of the sensing group 21 in one print wheelare aligned with the four holes of sensing groups in each of the otherprint wheels at rest in order for light from a source or sources 23 topass through all of the aligned sensing holes to a group of fourphotocells 24. When a pancake coil 25 in the latching plate 13 isenergized, the coil moves through a magnetic field provided by fourfixed magnets 26 26 mounted on a slotted aluminum support 28,. Endkeepers 28 and 28 of soft iron provide flux paths between the magnets ateach end as shown in FIG. 1. Current in the coil causes the plate 13 topivot about a point 29 away from the print wheel 10 to a positionagainst a stop 30 affixed to an upright portion of the support 28 Theshaft 11 then engages the print wheel 10 through the friction clutch 12to rotate it. As the alternate groups of sense and code holes pass thesense stations between the light source of sources and photocells, thecode groups of holes are detected.

When the code of the desired symbol is detected at the sense station,the coil 25 of the latching means is de-energized, thereby allowing thespring 15 to pivot the plate 13 back so that the arm 14 will re-engage aV notch and thereby index the selected symbol at the print station. Forexample, assuming the print station to be at the left as viewed in FIG.2, and that the numeral 1 is to be selected, the code group of holepositions for the numeral 1, enclosed by a dotted line block 31, aredetected at the sense station represented by a dotted line block 32 inFIG. 2. The inherent delay in deenergizing the latching means permitsthe code group of hole positions 31 for the numeral 1 to advance fromthe sense station 32 to the position shown in FIG. 2.

When in that position, the arm 14 of the latching means engages a Vnotch to align the numeral 1 for proper printing at the print stationassumed to be at the left.

It should be noted that the print station may be positioned any placewith respect to the latching means, such as opposite the latching meansas just assumed and illustrated in the arrangement of FIGS. 1 and 2, orat nearly a right angle which would place the print station at the topof FIG. 2. Positioning one relative to the other is completely arbitraryso long as the latching means engages a V notch with a selected symbolaligned for printing. It should also be noted that although the groupsof sense holes and code holes are uniformly spaced, with a group of codeholes halfway between two groups of sense holes, the group'of code holesmay be closer to one group of sense holes than the other, but the groupof sense holes should be uniformly spaced in order that the symbols andindexing V notches between symbols be uniformly spaced. And finally, itshould also be noted that although the sense holes are shown in radialalignment with the symbols on the periphery of the print wheel, that isnot necessary because the sense station may be positioned any place inrelation to the print station just so the print station is centered overa line of symbols while all wheels are at rest. What is important isthat having selected positions for the groups of code holes relative tothe symbols represented thereby, the sense station is positioned suchthat when a selected code group is detected, and the latching means istie-energized, the print wheel will be stopped with the symbol selectedat the print station.

FIG. 4 illustrates with sections of three print wheels 10 10, 10 and 10,the manner in which a code group 0011 is detected in the rotating printwheel 10 between stationary print wheels 10 and 10,-. A bit 0 in thecode is represented by the absence of a hole in a hole position in linewith holes of sense groups on the wheels 10 and 10 When the wheel 10 isin the position shown, and all other wheels are at rest with groups offour sense holes aligned, the output of the photodetectors will be fourdigital signals representing the code 0011, where the most significantbit is from the upper most photodetector.

The manner in which the data to be printed may be entered will now bedescribed with reference to FIG. 5. A data source '40 such as a keyboardor calculator enters the data into a register 41 in digital form. eitherserial by symbol and parallel by bit, or serial by symbol and serial bybit. For the example illustrated in FIG. 1, the symbols are specified by4-bit codes. Assuming an eleven place printer, the register 41 willconsist of 44 bit positions, a group of four bit positions for everysymbol position. A 4-bit code will provide for printing the numerals 1-9and 0, and four other symbols, such as a plus a minus a decimal pointand a blank (no print). It should be noted that every symbol positionmust be specified by a code having at least one hole, but not fourbecause four holes are used for the sense groups. The following is theassignment of codes illustrated in FIG.2.

CODE SYMBOL 0001 1 l0 2 OOH 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 91010 0 1011 1100 1101 1110 (BLANK) A 6-bit code would provide for theadditions of letters of the alphabet plus many other symbols forpunctuation, and still one more additional bit would provide for theaddition of both upper and lower case letters of the alphabet. Theprinciples illustrated for a 4-bit code would be the same for a 6 or7-bit code.

A bank of AND gates 42 couples the output of the register 41 to acomparator 43 (one symbol group at a time starting on the right) when aPRlNT command is issued by the data source 40. The command sets aflipflop 44 which in turn sets a flip-flop 45 and enables a group offour AND gates in the bank 42 to couple the 4-bit code of the firstsymbol to the comparator 43.

Once the flip-flop 45 is set, the solenoid of the latching means 13 forthe first print wheel 10, is energized, thereby releasing the firstprint wheel for rotation. When the code of the first symbol is detected,the comparator 43 transmits a signal through a power driver 46 to resetthe flip-flop 44 and the flip-flop 45, and to shift a commutating shiftregister 47. The bit 1 of the flipflop 44 then being reset is thusshifted into the register 47. The leading edge of the bit 1 shifted intothe register, i.e., the leading edge of the output of the first state ofthe register 47, sets a flip-flop 48 to release the next print wheel.That output of the register 47 also enables the next group of AND gatesin the bank 42 to couple the 4-bit code of the second symbol to thecomparator 43. When that code is detected in the second print wheel, theflip-flop 48 is reset and the bit-l in the shift register 47 isadvanced. The procedure is repeated until the last print wheel is reset,at which time the bit-l in the register 47 is shifted out as a printexecute signal, PRE.

The PRE signal is transmitted by an AND gate 50 (FIG. 6) to set aflip-flop 51 if the print roller 17 is a rest over a switch S That turnson transistors Q1, Q2 and O to apply current to a DC motor 52 of apolarity to drive a pulley 53 in a direction to move the roller to theright. Had the roller been at rest over a switch S,,, the flip-flop 51would have been reset via a gate 54 to turn on transistors Q4, Q5 and Oto drive the roller to the left. Power is applied to the motor 52 once aflipflop 55 is set directly by the leading edge of the signal, PRE, toturn on transistors Q and Q,,. When the roller 17 reaches the otherside, a switch A or B, is closed to transmit a step voltage, the leadingedge of which resets the flip-flop 55 via an OR gate 56. That ends onecomplete cycle of setting the print wheels and printing. Means (notshown) will then advance the paper from the supply roll 16 and advancethe printing ribbon 20. The means may be, for example, a stepping motorwhich operates through gear trains to advance the paper and ribbon theproper amount.

Although particular embodiments of the invention have been described andillustrated herein it is recognized that modifications and equivalentsmay readily occur to those skilled in the art. Consequently, it isintended that the claims be interpreted to cover such modifications andequivalents.

What is claimed is:

l. A printer employing a plurality of print wheels on a shaft, eachcarrying two sets of perforations, first set for coded groups ofperforations, each group in a predetermined pattern of perforationpositions, each coded group identifying by its position on the wheel asymbol on the print wheel, each group having N perforation positions andthe code being in the form of a unique combination of perforations andno perforations in said positions, and a second set of perforations ingroups, each group being arranged in said predeter mined pattern andhaving a hole in every position, each group in said second set beingavailable for sensing the coded groups on a turning print wheel whileall other print wheels are at rest, each with a symbol in proper alignedposition for printing at a printing stations, means for rotating oneprint wheel at a time while the rest of the print wheels are stationarywith a group of sensing perforations in each stationary wheel in linewith a group of sensing perforations in all other stationary wheels forpermitting light to pass through all sensing perforations of alignedgroups of said second set to N photocells, one photocell for eachperforation position at one end of said shaft, said light beinginterrupted only by said coded groups of perforations of said first setof perforations in said turning print wheel as they rotate past saidsensing groups in line with said photocells, each of said coded groupsbeing disposed to have its perforation positions to be in line withperforation positions of said aligned sensing groups in stationarywheels as said turning wheel brings each coded group into a position toblock light to said photocells.

2. A printer as defined in claim 1 including a comparator connected toreceive signals from said photocells for comparison with a coded groupof N signals specifying a symbol to be positioned at said printingstation, and means responsive to said comparator for stopping saidturning wheel when signals produced in said photocells in response tothe interruption of light by a unique coded group of perforationscoincide with said signals to said comparator specifying the symbol tobe printed, whereby a symbol identified by the position of said uniquecoded group of perforations is positioned at said print station.

3. A printer as defined in claim 2 wherein said means for turning oneprint wheel at a time is comprised of means for turning said shaft, aslip clutch coupling each print wheel to said shaft, separate means forholding each print wheel in a stationary position, a separate uctuatingmeans for each holding means responsive to a control signal for causingsaid holding means to release a print wheel for rotation, and means forremoving said control signal from an actuating means when saidcomparator detects coincidence.

4. in a printer having a plurality of axially aligned print wheels, eachto be individually set with a selected symbol on the circumferentialsurface thereof in an indexed position at a print station in line withsymbols similarly set on all other print wheels, an improved apparatusfor setting said print wheels comprised of:

a first set of perforations in said wheel arranged in uniformly spacedgroups, each group consisting of a plurality of perforations in aparticular pattern such'that perforations of all groups coincide withperforations of groups in adjacent print wheels when at rest withsymbols in said indexed position,

a second-set of. perforations in said wheels arranged in groups of oneto N perforations in a pattern of perforationpositions coinciding with Nperforations of a group in said first set in an adjacent print wheelwhen one is rotated relative to the other to bring the two groupsopposite each other, said groups of said second set being interspacedwith said groups of said first set, and each group of said second sethaving a unique combination of perforations according to a predeterminedcode, every unique combination specifying a symbol on said surface byits spatial relationship therewith, said relationship being the same forevery code group and symbol combination,

means for transmitting light through one group of said first'set of eachstationary print wheel in alignment,

a set of N photocells for detecting light through N perforations of saidaligned groups of said stationary wheels, said photocells being arrangedin a pattern corresponding to said pattern of perforation positions ofsaid coded groups in said second set,

means for providing a group of N coded digital signals for specifying asymbol on a particular print wheel to be positioned at said printstation,

means forcomparing said group of N coded digital signals with outputsignals from said photocells, and

means for turning the print wheel to be positioned with said specifiedsymbol in said print station until said comparing means detects acoincidence between output signals of said photocells and said group ofN coded digital signals specifying said symbol.

5. A printer comprising: i

a plurality of print wheels, each carrying two sets of perforationsarranged in radially aligned groups, each group having one or moreperforations, all groups of a first set having a minimum number, N, ofperforations in a fixed pattern for use as light paths through allaxially aligned print wheels while at rest in an indexed position duringthe sensing of coded groups of a second set interspaced between groupsof said first set in one of said print wheels while being selectivelycaused to rotate, each code group of said second set uniquelyidentifying a symbol, each symbol being positioned withthe same spatialrelationship to the code group of perforations which uniquely identifiesit,

a shaft and means for rotating said shaft, each of said print wheelsbeing axially mounted on said shaft and coupled to said shaft by afriction clutch,

a plurality of latching means, a separate one for each print wheel forholding said print wheels at rest in said indexed position with aselected one of said symbols on one print wheel in line with all othersymbols selected on other wheels for printing at a print station,

means for directing light through N light paths provided by a group ofperforations of said first set in one print wheel at rest aligned withgroups of perforations of said first set in all other print wheels atrest,

a number of photocells, one for each of said N light paths positioned toreceive light in said paths, means for providing a group of N codeddigital signals for specifying a symbol on a particular print wheel tobe positioned at said print station, means for individually unlatchingsaid latching means for said particular print wheel,

means for comparing said coded signals specifying a symbol to beselected with coded signals produced by said photocells in response toperforations of said coded groups in said particular print wheelinterrupting said light paths, and

means responsive to said comparator for causing said latching means toagain hold said particular wheel stationary, whereby said latching meansstops said rotating wheel in a position with said specified symbol onthe circumferential surface thereof in said print position at said printstation.

6. In a printer comprised of a plurality of print wheels on acommon-shaft, each print wheel being divided into a plurality of sectorsand having a plurality of symbols. one symbol on every other sector, animproved mechanism for positioning said wheels individually to printdesired symbols through the use of groups of coded perforations in saidprint wheels, each of said print wheels having coded perforations inpredetermined positions, one group of coded perforations for each symbolin a sector of said wheel, each intermediate sector between every pairof adjacent coded sectors having a perforation in the position of everypermissible perforation of each of said code groups, means fortransmitting a light beam through each permissible perforation of eachof said code groups in an intermediate sector of each print wheel whilestationary with intermediate sectors aligned, means for rotating oneprint wheel at a time, means for individually positioning said printwheels as they are rotated, one at a time. by sensing said lighttransmitted through code perforations in a turning wheel and throughaligned perforations in intermediate sectors of all other wheels whichare stationary, and bringing said turning wheel to rest with itsintermediate sectors aligned with intermediate sectors of all otherwheels.

7. A low cost printer comprising a plurality of print wheels arrangedside by side on a common shaft, each with symbols on the circumferentialsurface thereof and V notches on that surface between symbols, saidnorches being provided for the purpose of holding said print wheels inan indexed position with a symbol of each in proper alignment withsymbols of all other print wheels at a print station, each print wheelbeing provided with two sets of perforations each set comprising aplurality of grouped perforations, each group having one or moreperforations in a fixed pattern of perforations, all groups of one sethaving at least N perforations for use only as light paths in sensingcoded groups of the other set in one rotating print wheel while allother print wheels are held stationary in an indexed position, theperforations in N perforation positions of the groups in the second setbeing in the same pattern as the N perforation positions of groups inthe first set, and perforations in groups of said second set beingprovided in said positions in accordance with a predetermined code touniquely identify symbols by relative position on the print wheel,whereby all perforations in said positions of groups of the first set inone wheel are in line with corresponding positions of all groups of thefirst set of all other wheels while stationary in said indexed positionin order that one group of every wheel will be in line to form N lightbeam paths from a source, or sources, illuminating N photocells at oneend of said print wheels arranged side by side, means for rotating oneprint wheel at a time, thereby sensing coded groups of perforations inthe rotating print wheel as the coded groups of perforation positions onthe rotating print wheel pass through a position of alignment with saidN light beam paths, means for designating a symbol code for saidrotating print wheel, and means for stopping said rotating print wheelwhen the designated symbol code is detected by said photocells.

8. Apparatus as defined in claim 7 wherein said common shaft is beingrotated continuously by a motor and said print wheels are heldstationary by individual latching means, each of said print wheels beingcoupled to said shaft by a separate friction clutch, thus causing codegroups on one rotating wheel to be driven past the aligned perforationsof the remaining print wheels held stationary until the designated codeof a symbol is detected by said photocells.

9. Apparatus as defined in claim 8 wherein the position of the latchingmeans relative to the photocells is such as to stop the rotating printwheel with the selected symbol in a print position.

10. Apparatus as defined in claim 9 wherein V notches are providedbetween symbols on said wheels and said latching means comprises apointed arm which fits into a V notch thereby assuring the selectedsymbol will come to rest in proper alignment at the print sta-

1. A printer employing a plurality of print wheels on a shaft, eachcarrying two sets of perforations, first set for coded groups ofperforations, each group in a predetermined pattern of perforationpositions, each coded group identifying by its position on the wheel asymbol on the print wheel, each group having N perforation positions andthe code being in the form of a unique combination of perforations andno perforations in said positions, and a second set of perforations ingroups, each group being arranged in said predetermined pattern andhaving a hole in every position, each group in said second set beingavailable for sensing the coded groups on a turning print wheel whileall other print wheels are at rest, each with a symbol in proper alignedposition for printing at a printing stations, means for rotating oneprint wheel at a time while the rest of the print wheels are stationarywith a group of sensing perforations in each stationary wheel in linewith a group of sensing perforations in all other stationary wheels forpermitting light to pass through all sensing perforations of alignedgroups of said second set to N photocells, one photocell for eachperforation position at one end of said shaft, said light beinginterrupted only by said coded groups of perforations of said first setof perforations in said turning print wheel as they rotate past saidsensing groups in line with said photocells, each of said coded groupsbeing disposed to have its perforation positions to bE in line withperforation positions of said aligned sensing groups in stationarywheels as said turning wheel brings each coded group into a position toblock light to said photocells.
 2. A printer as defined in claim 1including a comparator connected to receive signals from said photocellsfor comparison with a coded group of N signals specifying a symbol to bepositioned at said printing station, and means responsive to saidcomparator for stopping said turning wheel when signals produced in saidphotocells in response to the interruption of light by a unique codedgroup of perforations coincide with said signals to said comparatorspecifying the symbol to be printed, whereby a symbol identified by theposition of said unique coded group of perforations is positioned atsaid print station.
 3. A printer as defined in claim 2 wherein saidmeans for turning one print wheel at a time is comprised of means forturning said shaft, a slip clutch coupling each print wheel to saidshaft, separate means for holding each print wheel in a stationaryposition, a separate actuating means for each holding means responsiveto a control signal for causing said holding means to release a printwheel for rotation, and means for removing said control signal from anactuating means when said comparator detects coincidence.
 4. In aprinter having a plurality of axially aligned print wheels, each to beindividually set with a selected symbol on the circumferential surfacethereof in an indexed position at a print station in line with symbolssimilarly set on all other print wheels, an improved apparatus forsetting said print wheels comprised of: a first set of perforations insaid wheel arranged in uniformly spaced groups, each group consisting ofa plurality of perforations in a particular pattern such thatperforations of all groups coincide with perforations of groups inadjacent print wheels when at rest with symbols in said indexedposition, a second set of perforations in said wheels arranged in groupsof one to N perforations in a pattern of perforation positionscoinciding with N perforations of a group in said first set in anadjacent print wheel when one is rotated relative to the other to bringthe two groups opposite each other, said groups of said second set beinginterspaced with said groups of said first set, and each group of saidsecond set having a unique combination of perforations according to apredetermined code, every unique combination specifying a symbol on saidsurface by its spatial relationship therewith, said relationship beingthe same for every code group and symbol combination, means fortransmitting light through one group of said first set of eachstationary print wheel in alignment, a set of N photocells for detectinglight through N perforations of said aligned groups of said stationarywheels, said photocells being arranged in a pattern corresponding tosaid pattern of perforation positions of said coded groups in saidsecond set, means for providing a group of N coded digital signals forspecifying a symbol on a particular print wheel to be positioned at saidprint station, means for comparing said group of N coded digital signalswith output signals from said photocells, and means for turning theprint wheel to be positioned with said specified symbol in said printstation until said comparing means detects a coincidence between outputsignals of said photocells and said group of N coded digital signalsspecifying said symbol.
 5. A printer comprising: a plurality of printwheels, each carrying two sets of perforations arranged in radiallyaligned groups, each group having one or more perforations, all groupsof a first set having a minimum number, N, of perforations in a fixedpattern for use as light paths through all axially aligned print wheelswhile at rest in an indexed position during the sensing of coded groupsof a second set interspaced between groups of said first set in one Ofsaid print wheels while being selectively caused to rotate, each codegroup of said second set uniquely identifying a symbol, each symbolbeing positioned with the same spatial relationship to the code group ofperforations which uniquely identifies it, a shaft and means forrotating said shaft, each of said print wheels being axially mounted onsaid shaft and coupled to said shaft by a friction clutch, a pluralityof latching means, a separate one for each print wheel for holding saidprint wheels at rest in said indexed position with a selected one ofsaid symbols on one print wheel in line with all other symbols selectedon other wheels for printing at a print station, means for directinglight through N light paths provided by a group of perforations of saidfirst set in one print wheel at rest aligned with groups of perforationsof said first set in all other print wheels at rest, a number ofphotocells, one for each of said N light paths positioned to receivelight in said paths, means for providing a group of N coded digitalsignals for specifying a symbol on a particular print wheel to bepositioned at said print station, means for individually unlatching saidlatching means for said particular print wheel, means for comparing saidcoded signals specifying a symbol to be selected with coded signalsproduced by said photocells in response to perforations of said codedgroups in said particular print wheel interrupting said light paths, andmeans responsive to said comparator for causing said latching means toagain hold said particular wheel stationary, whereby said latching meansstops said rotating wheel in a position with said specified symbol onthe circumferential surface thereof in said print position at said printstation.
 6. In a printer comprised of a plurality of print wheels on acommon shaft, each print wheel being divided into a plurality of sectorsand having a plurality of symbols, one symbol on every other sector, animproved mechanism for positioning said wheels individually to printdesired symbols through the use of groups of coded perforations in saidprint wheels, each of said print wheels having coded perforations inpredetermined positions, one group of coded perforations for each symbolin a sector of said wheel, each intermediate sector between every pairof adjacent coded sectors having a perforation in the position of everypermissible perforation of each of said code groups, means fortransmitting a light beam through each permissible perforation of eachof said code groups in an intermediate sector of each print wheel whilestationary with intermediate sectors aligned, means for rotating oneprint wheel at a time, means for individually positioning said printwheels as they are rotated, one at a time, by sensing said lighttransmitted through code perforations in a turning wheel and throughaligned perforations in intermediate sectors of all other wheels whichare stationary, and bringing said turning wheel to rest with itsintermediate sectors aligned with intermediate sectors of all otherwheels.
 7. A low cost printer comprising a plurality of print wheelsarranged side by side on a common shaft, each with symbols on thecircumferential surface thereof and V notches on that surface betweensymbols, said norches being provided for the purpose of holding saidprint wheels in an indexed position with a symbol of each in properalignment with symbols of all other print wheels at a print station,each print wheel being provided with two sets of perforations each setcomprising a plurality of grouped perforations, each group having one ormore perforations in a fixed pattern of perforations, all groups of oneset having at least N perforations for use only as light paths insensing coded groups of the other set in one rotating print wheel whileall other print wheels are held stationary in an indexed position, theperforations in N perforation positions of the groups in the second setbeing in the same pattern as the N perforation positions of groups inthe first set, and perforations in groups of said second set beingprovided in said positions in accordance with a predetermined code touniquely identify symbols by relative position on the print wheel,whereby all perforations in said positions of groups of the first set inone wheel are in line with corresponding positions of all groups of thefirst set of all other wheels while stationary in said indexed positionin order that one group of every wheel will be in line to form N lightbeam paths from a source, or sources, illuminating N photocells at oneend of said print wheels arranged side by side, means for rotating oneprint wheel at a time, thereby sensing coded groups of perforations inthe rotating print wheel as the coded groups of perforation positions onthe rotating print wheel pass through a position of alignment with saidN light beam paths, means for designating a symbol code for saidrotating print wheel, and means for stopping said rotating print wheelwhen the designated symbol code is detected by said photocells. 8.Apparatus as defined in claim 7 wherein said common shaft is beingrotated continuously by a motor and said print wheels are heldstationary by individual latching means, each of said print wheels beingcoupled to said shaft by a separate friction clutch, thus causing codegroups on one rotating wheel to be driven past the aligned perforationsof the remaining print wheels held stationary until the designated codeof a symbol is detected by said photocells.
 9. Apparatus as defined inclaim 8 wherein the position of the latching means relative to thephotocells is such as to stop the rotating print wheel with the selectedsymbol in a print position.
 10. Apparatus as defined in claim 9 whereinV notches are provided between symbols on said wheels and said latchingmeans comprises a pointed arm which fits into a V notch thereby assuringthe selected symbol will come to rest in proper alignment at the printstation.